To Join Together
To Unify, To Match
You know that the alternative kanji meaning for 合 is join, which is what we're using here. The verb form of join is to join together, and it can also mean to unify and to match.
あわせる
The reading comes from 合う, so if you know that reading you'll know this reading as well.
全ての赤と白のワイヤーを一たばに合わせました。
We joined all the red and white wires together.
男が女のペースに合わせてゆっくり歩くのは、その女のことが好きな時だけさ。
A man will only slow down to match a woman's pace if they like her.
おい、スティーヴ！お前はもうずいぶん長く日本に住んでいるんだから、そろそろ日本の習慣とかに合わせたほうがいいんじゃないのか？好き嫌いは止めて、魚も食べるようにしろよ！
Hey, Steve. You’ve been living in Japan for a pretty long time now so don’t you think it’s time for you to adjust to Japanese customs? Stop being so picky and start eating fish.